1. Field of Invention
The present invention relates to liquid crystal devices used in electrophotographic printers as light valves and, and in particular, to the multiplexing of electronic drivers for a liquid crystal device in a printer.
2. Description of the Prior Art
In a typical transmissive type, liquid crystal device, a thin layer of liquid crystal material is sandwiched between parallel, transparent glass substrates bearing transparent, patterened electrodes on their inner confronting surfaces. At least one polarizer is located on the outer surface of one of the glass substrates and a light source spaced from the device directs light therethrough. By selectively applying an electric field across the layer of liquid crystal material by means of selectively applying an AC voltage to the electrodes, the transmissivity of the liquid crystal device may be changed for passing or blocking light in accordance with the electrodes addressed by the voltage. It is known, as disclosed in U.S. Pat. No. 4,595,259 assigned to the same assignee as the present invention, that the transient response of a liquid crystal light valve can be used as an image bar for the purpose of printing optical images on xerographic drums.
The prior art is replete with multiplexing driving circuits, in particular, as applied to liquid crystal displays, for example, U.S. Pat. Nos. 3,786,486, 3,873,537, 4,427,798, and 4,308,534. The above-identified references, however, are for use with a display system. Thus, in the display mode, a part of the display is strobed and this information is written on a line. The line is then left in an unaccessed state until the next strobe pulse. During this unaccessed period, in the above-identified references, it is important that the information remain displayed as long as possible to make efficient use of the illuminating light source.
It would be desirable, however, to provide a multiplexing system for use in a print bar system rather than in a display system, and to provide a multiplexing system to reduce the number of drivers. It is still another object of the present invention to place a section of the printer in an unaccessed state while another section of the printer begins printing in in order to have no data displayed which would be blurred or smeared. Further objects and advantages of the present invention will become apparent as the following description proceeds and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.